Alternator fusing

[peterg]

I am replacing the control box for a fuse box, having rigged up an alternator (I hope the lower mounting lasts).
I've got an eight line fuse box to fit.
Can anyone suggest what size fuses I should use with each of the output wires?
Regards, Peter

[Ferrington G]

I use 25 which seem to work.

[peterg]

Thanks, I was rather hoping to match the fuse size more closely to the circuit load as I will be installing about 6 fuses

[Bristolian]

Hi Peter

You are quite right in asking which fuse you should use as the loading will vary. I have forwarded your thread to a member of our technical team who is best suited to give you a detailed explanation as he worked for the electrical development department of a major motor manufacturer.

John Lawley
Spares & Technical Support Officer
BODA

[phillip408/2]

Hi peterg

Just had a message from John Lawley who has passed this on to me, as I am Technical Support of all things electrical in the Bristol Owners & Drivers Association - BODA.

You did not specify what circuits you are fusing. I youf can be more specific I will endeavour to answer your queries.

Kind regards

Phillip

[peterg]

Phillip,
I am replacing the control box which has two 35 amp fuses with a fuse box, so it is the wires that go into the box.
Sorry to sound vague but the car is miles away and I only have the control box to look at.
The car has been rewired and is negative earth. I intend to take the alternator output direct to the starter solenoid and feed back to the fuse box, so it is the outputs from the A terminals that I need to fuse. Looking at the wiring diagram I must admit that I cannot easily identify what equipment they go to, or their loads. I have read that the blower takes a lot of power.
Regards, Peter

[phillip408/2]

Hi Peter

I assume that you are fitting a fiveway fusebox with standard glass fuses. The ratings of these fuses are misleading, as the Lucas 35 amp fuse, will carry about half of the rating before they warm up and melt, so the 35amp really means that this is the current at which the fuse will blow at.

The two way fuse block as fitted to the majority of 50s and 60s cars, was for a fused 12 volt supply to accessories, and a fused 12 volt supply for ignition switched circuits. Often, both fuses were 35 amp.

The accessories fuse is supplied with a thick Brown cable on one side, and after the fuse the cable colour is Purple.

Likewise, the ignition fuse is fed by a thick White cable, and after the fuse the cable colour is Green.

Before you allocate the cables to the fuses, you will have to determine what each one powers up. When you have tagged them, I suggest that you divide the circuits up as follows;

Two fuses for the Accessories (1) rated at 10 amps (Lucas 20A)

Radio, Clock & Interior Lights

(2) rated at 17.5 amps (Lucas 35A)

Horns & Cigar Lighter ,(Fog lamp if fitted)

Three fuses for Ignition controlled circuits:

(1) rated at 17.5 amps (Lucas 35A)

Wiper Motor & Heater Blower

(2) rated at 10 amps (Lucas 20A)

Fuel Gauge, Direction Indicators,
Reversing Lights,
(Brake Fluid Warning if fitted)

(3) rated at 17.5 amps (Lucas 35A)

Cooling Fans

I hope that this info is of some use to you.

Kind regards

Phillip

[peterg]

Thank you Phillip. That might explain why the Lucas fuse has fuse wire while the other has a thick piece of metal down it.

I will be fitting the continental ceramic type of fuse. From what you have said I will fit the lower amperages quoted.

Regards, Peter

[James McClure]

This panel attaches to the back of the dash, so is unseen. On the other side of the panel are three relays. I found that a relay is needed for the electric fan, at the least. Often the charging and ignition wires are not fused.